Convergence correction circuit and three tube type projector having the

Abstract

A convergence correction circuit for use in a projection CRT of the electrostatic focusing type, including a neck portion provided with a sub-deflection yoke for convergence correction. A coupling correction filter and an eddy current correction filter are interposed between a path of a convergence correction signal. The coupling correction filter corrects a change in correction frequency characteristic due to an influence of coupling of a sub-deflection yoke and a deflection yoke, and the eddy current correction filter corrects a change in correction frequency characteristic due to an influence of an eddy current caused in an electrostatic convergence electrode by a magnetic field generated in the sub-deflection yoke. When a coil of the sub-deflection yoke is supplied with a current proportional to an output of the correction filter, convergence correction is performed. There is obtained correction frequency characteristic which is flat, so that a motion of an image on a fluorescent screen of the cathode-ray tube coincides with a wave form of a correction signal. Therefore, high-precision convergence correction can be obtained.